Spatial bridges and the spread of Chlamydia: the case of a county in Sweden

Ten years transmission of the new variant of Chlamydia trachomatis in Sweden: prevalence of infections and associated complications

OBJECTIVES

In 2006, a new variant of Chlamydia trachomatis (nvCT) was discovered in Sweden. It has a deletion in the plasmid resulting in failed detection by the single target systems from Abbott and Roche used at that time, whereas the third system used, from Becton Dickinson (BD), detects nvCT. The proportion of nvCT was initially up to 65% in counties using Abbott/Roche systems. This study analysed the proportion of nvCT from 2007 to 2015 in four selected counties and its impact on chlamydia-associated complications.

METHODS

C. trachomatis-positive specimens collected from 2007 to 2015 were analysed by a specific PCR to identify nvCT cases. Genotyping was performed by multilocus sequence typing (MLST) and ompA sequencing. Ectopic pregnancy and pelvic inflammatory disease records were extracted from the national registers.

RESULTS

In total, 5101 C. trachomatis-positive samples were analysed. The nvCT proportion significantly decreased in the two counties using Roche systems, from 56% in 2007 to 6.5% in 2015 (p<0.001). In the two counties using BD systems, a decrease was also seen, from 19% in 2007 to 5.2% in 2015 (p<0.001). Fifteen nvCT cases from 2015 and 102 cases from 2006 to 2009 had identical MLST profiles. Counties using Roche/Abbott systems showed higher mean rates of ectopic pregnancy and pelvic inflammatory disease compared with counties using BD systems.

CONCLUSIONS

The nvCT proportion has decreased in all counties and converged to a low prevalence irrespective of previous rates. Genotyping showed that nvCT is clonal and genetically stable. Failing detection only marginally affected complication rates.

Structural bridging network position is associated with HIV status in a younger Black men who have sex with men epidemic

Younger Black men who have sex with men (BMSM) ages 16-29 have the highest rates of HIV in the United States. Despite increased attention to social and sexual networks as a framework for biomedical intervention, the role of measured network positions, such as bridging and their relationship to HIV risk has received limited attention. A network sample (N = 620) of BMSM respondents (N = 154) and their MSM and transgendered person network members (N = 466) was generated through respondent driven sampling of BMSM and elicitation of their personal networks. Bridging status of each network member was determined by a constraint measure and was used to assess the relationship between this bridging and unprotected anal intercourse (UAI), sex-drug use (SDU), group sex (GS) and HIV status within the network in South Chicago. Low, moderate and high bridging was observed in 411 (66.8 %), 81 (13.2 %) and 123 (20.0 %) of the network. In addition to age and having sex with men only, moderate and high levels of bridging were associated with HIV status (aOR 3.19; 95 % CI 1.58-6.45 and aOR 3.83; 95 % CI 1.23-11.95, respectively). Risk behaviors observed including UAS, GS, and SDU were not associated with HIV status, however, they clustered together in their associations with one another. Bridging network position but not risk behavior was associated with HIV status in this network sample of younger BMSM. Socio-structural features such as position within the network may be important when implementing effective HIV prevention interventions in younger BMSM populations.

Sexual networks, surveillance, and geographical space during syphilis outbreaks in rural North Carolina

BACKGROUND

Sexually transmitted infections (STIs) spread along sexual networks whose structural characteristics promote transmission that routine surveillance may not capture. Cases who have partners from multiple localities may operate as spatial network bridges, thereby facilitating geographical dissemination. We investigated how surveillance, sexual networks, and spatial bridges relate to each other for syphilis outbreaks in rural counties of North Carolina.

METHODS

We selected from the state health department's surveillance database cases diagnosed with primary, secondary, or early latent syphilis during October 1998 to December 2002 and who resided in central and southeastern North Carolina, along with their sex partners and their social contacts irrespective of infection status. We applied matching algorithms to eliminate duplicate names and create a unique roster of partnerships from which networks were compiled and graphed. Network members were differentiated by disease status and county of residence.

RESULTS

In the county most affected by the outbreak, densely connected networks indicative of STI outbreaks were consistent with increased incidence and a large case load. In other counties, the case loads were low with fluctuating incidence, but network structures suggested the presence of outbreaks. In a county with stable, low incidence and a high number of cases, the networks were sparse and dendritic, indicative of endemic spread. Outbreak counties exhibited densely connected networks within well-defined geographic boundaries and low connectivity between counties; spatial bridges did not seem to facilitate transmission.

CONCLUSIONS

Simple visualization of sexual networks can provide key information to identify communities most in need of resources for outbreak investigation and disease control.

Identification of potential opinion leaders in child health promotion in Sweden using network analysis

BACKGROUND

Opinion leaders are often local individuals with high credibility who can influence other people. Robust effects using opinion leaders in diffusing innovations have been shown in several randomized controlled trials, for example regarding sexually transmitted infections (STI), human immunodeficiency virus (HIV) prevention, mammography rates and caesarean birth delivery rates. In a Cochrane review 2010 it was concluded that the use of opinion leaders can successfully promote evidence-based practice. Thus, using opinion leaders within the public health sector might be one means to speed up the dissemination of health promoting and disease preventing innovations. Social network analysis has been used to trace and map networks, with focus on relationships and positions, in widely spread arenas and topics. The purpose of this study was to use social network analysis in order to identify potential opinion leaders at the arena of child health promotion in Sweden.

RESULTS

By using snowball technique a short e-mail question was spread in up to five links, starting from seven initially invited persons. This inquiry resulted in a network consisting of 153 individuals. The most often mentioned actors were researchers, public health officials and paediatricians, or a combination of these professions. Four single individuals were mentioned by five to seven other persons in the network. These individuals obviously possess qualities that make other professionals within the public health sector listen to and trust them.

CONCLUSIONS

Social network analysis seemed to be a useful method to identify influential persons with high credibility, i.e. potential opinion leaders, at the arena of child health promotion in Sweden. If genuine opinion leaders could be identified directed measures can be carried out in order to spread new and relevant knowledge. This may facilitate for public health actors at the local, regional and national level to more rapidly progress innovations into everyday practice. However, effectiveness studies of opinion leaders in the public health sector still have to be performed.

Prevalence trends in Sweden for the new variant of Chlamydia trachomatis

In 2006, a new variant of Chlamydia trachomatis (nvCT) was discovered in Sweden that was not detectable with Abbott m2000 (Abbott) and Amplicor/COBAS Amplicor/TaqMan48 (Roche). The proportion of nvCT was 20-64% of the detected Chlamydia cases in counties using Abbott/Roche test systems. Although the ProbeTec system from Becton Dickinson (BD) could detect nvCT, the proportion of nvCT in counties using BD was 7-19%. The objective of the current study was to follow the nvCT proportions from 2007 to 2009 in two counties that used Roche and had introduced test systems able to detect nvCT in late 2006. The nvCT was also followed in two counties that used BD, and in all four counties the effect of nvCT on the serotype distribution of C. trachomatis wild-type strains was analysed. A total of 2576 specimens positive for C. trachomatis were collected in the four counties at three time points, and analysed for nvCT and serotype E. The proportion of nvCT declined significantly in the two counties using Roche, from 65% and 48% in 2007 to 24% for both counties in 2009 (p <0.001). The nvCT proportion increased in Norrbotten county, which used BD, from 9% in 2007 to 19% in 2009 (p 0.03). In Uppsala county, which also used BD but was surrounded by counties using detection systems from Roche, the proportion of nvCT declined from 24% in 2007 to 18% in 2009 (p <0.03). No major difference in the level of serotype E was seen. The proportion of nvCT seems to rapidly converge in the Swedish counties after the selective diagnostic advantage for nvCT has been lost in the Abbott/Roche counties.

The Swedish new variant of Chlamydia trachomatis

PURPOSE OF REVIEW

This review focuses on the anatomy of the Swedish new variant of Chlamydia trachomatis (nvCT). This information provides an interesting insight into the emergence of new strains (how, where, and when), and the important lessons learned are discussed.

RECENT FINDINGS

In late 2006, the nvCT was first reported in Sweden; it carries a 377 bp deletion within its plasmid which covers the single targets originally used by Roche and Abbott diagnostic systems. The nvCT spread rapidly with thousands of falsely negative diagnoses. Genome sequencing and phenotypic characterization showed that the biological fitness of nvCT when compared with wild-type CT in vitro is unaltered. Therefore, the rapid transmission of nvCT was due to the selective advantage gained from failed diagnosis and the introduction of nvCT into a high-frequency transmitting population. The proportions of nvCT cases are now converging toward equilibrium with the wild-type CT strains. Interestingly, the nvCT remains rarely reported beyond the Nordic countries.

SUMMARY

The spread of nvCT had a substantial impact on C. trachomatis identification, epidemiology, and public health in Sweden. Lessons learned from this experience include the importance of investigating the incidence and epidemiology of infection in detail, the frequent participation in appropriate quality assurance schemes, and the careful design of diagnostic assays. The nvCT presents a unique opportunity to study the spread of a single C. trachomatis strain within both the human and bacterial populations; this may substantially increase our knowledge of epidemiology and transmission of chlamydial infections, and other sexually transmitted infections.

[The Swedish Chlamydia mutant nvC trachomatis in Norway]

BACKGROUND

A mutant Chlamydia trachomatis variant (nvC trachomatis) has made it more difficult to diagnose chlamydia in Sweden. The proportion of nvC trachomatis has varied between Swedish counties (25-80 %) in the period 2006-07. Our goal has been to monitor nvC trachomatis among our patients from January 2007 and up to July 2008.

MATERIAL AND METHODS

In this time period, all C trachomatis samples at Fürst Medical Laboratory, Norway were analyzed twice. Cobas TaqMan 48 (Roche Diagnostics) was used to detect C trachomatis in isolated DNA and real-time PCR methods developed by us were used to both detect and verify nvC trachomatis.

RESULTS

61 patients of 23 726 patients were identified as carriers of nvC trachomatis. The proportion of C trachomatis carriers who were positive for nvC trachomatis increased from 1.0 % in the first quarter of 2007 to 3.2 % in the second quarter of 2008.

INTERPRETATION

Our results show a slow but steady increase in the proportion of nvC trachomatis positive tests. As compared to previous rates reported in Sweden (25-80 %), the occurrence of nvC trachomatis in our data is low. The epidemiology of this chlamydia mutant contributes to the understanding of mechanisms for spread of sexually transmitted infections and emphasize that you only find what you are looking for.

Information dynamics shape the sexual networks of Internet-mediated prostitution

Like many other social phenomena, prostitution is increasingly coordinated over the Internet. The online behavior affects the offline activity; the reverse is also true. We investigated the reported sexual contacts between 6,624 anonymous escorts and 10,106 sex buyers extracted from an online community from its beginning and six years on. These sexual encounters were also graded and categorized (in terms of the type of sexual activities performed) by the buyers. From the temporal, bipartite network of posts, we found a full feedback loop in which high grades on previous posts affect the future commercial success of the sex worker, and vice versa. We also found a peculiar growth pattern in which the turnover of community members and sex workers causes a sublinear preferential attachment. There is, moreover, a strong geographic influence on network structure--the network is geographically clustered but still close to connected, the contacts consistent with the inverse-square law observed in trading patterns. We also found that the number of sellers scales sublinearly with city size, so this type of prostitution does not, comparatively speaking, benefit much from an increasing concentration of people.

Sexual networks are diverse and complex: prevalence of relationships bridging population subgroups in the Seattle Sex Survey

GOAL

To better understand how and how often individuals bridge demographic groups in their sex partnerships, and to describe the epidemiologic characteristics of bridging and associations with history of sexually transmitted infection (STI).

METHODS

We describe the frequency of different hypothetical sexual bridging types among men and women aged 18 to 39 participating in a random digit dialing survey conducted in 2003 to 2004, and the associations of bridging behavior with risk factors for and self-reported history of STI.

RESULTS

Of the 1013 participants who described their 2 most recent sexual partnerships, 753 (74%), were classified as a bridge of some type. Education bridges were most prevalent (46%), followed by spatial (34%), age (29%), race (24%), and gender bridges (3%).

CONCLUSIONS

Sexual networks are diverse and complex, and there are multiple potential paths for infection flow.